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Grading on a Partisan Curve

The divide between liberals and conservatives applies to more than just attitudes about the role of government. It appears to make a difference in university grading, too.

A new study by Talia Bar and Asaf Zussman looked at patterns in how Republican and Democratic college professors graded students. It is based on a data set of grades, courses and SAT scores of 17,062 students at an unnamed “elite university.” The researchers then determined the political affiliation of the professors assigning those grades, based on listings on local voter registration rolls (for the 511 professors who were registered with a party, anyway).

The authors were interested in whether Democrats professors gave out a more egalitarian distribution of grades, since liberals believe more strongly than conservatives “in the justification for governmental action to reduce inequality.”

And their hunch appears to be right.

Here’s a chart, taken from the paper, that shows the average grades given to students who had scored in a few different SAT ranges. The dashed line shows Republican professors’ grades, and the solid line shows Democratic professors’ grades:

As you can see, the grading distribution for Democratic professors is relatively flat, meaning there was little variety in grades assigned to students with different SAT scores. The Republican line is steeper, meaning that Republicans had more variance in their grading: They gave both more A’s and more D’s than Democrats did; Democrats tend to give a lot of B’s.

From the paper:

[T]he share of the lowest grades (F, D-, D, D+, and C-) out of the total is 6.2 percent in courses taught by Republican professors and only 4.0 percent in courses taught by Democratic professors; the share of the highest grade (A+) out the total is 8.0 percent in courses taught by Republican professors and only 3.5 percent in courses taught by Democratic professors. Both differences are highly statistically significant.

The study’s authors suggest that the egalitarianism, or lack thereof, shown by these two groups of professors may reflect their different worldviews.

There are some major caveats to this finding, including that the sample size for Republican professors was much smaller than that for Democratic professors. There are also many ways to interpret this difference in grading, including that students may actually perform differently in classes taught by a professor from one party versus the other.

In any case, I recommend checking out the paper, which is to be published by The American Economic Journal: Applied Economics. It also observes that black students receive significantly lower grades than white students when taking a course with a Republican professor as opposed to a Democratic one — but again, the reasons are open to interpretation.

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